1. Field of the Invention
This invention relates to a method of processing a radiographic image used for medical diagnosis and an apparatus therefor, and more particularly to a method of and apparatus for processing a radiographic image when the radiographic image once recorded on a radiographic film is copied on a recording medium. The image processing method and apparatus of this invention performs an unsharp masking process on the radiographic image to enhance the diagnostic efficiency and accuracy of the radiographic image.
The radiographic image referred to in this application means an original X-ray image recorded on an X-ray film by the conventional radiographic method. The present invention is applied to the radiographic image copying system in which the radiographic image is once converted to an electric signal and the electric signal is used for reproducing the radiographic image on a final recording medium like an ordinary photographic film. When the electrical signal is used for reproducing the radiographic image, the electric signal is processed to obtain an improved image having high diagnostic efficiency and accuracy.
2. Description of the Prior Art
Since X-rays do harm to the human body, it is impossible from the viewpoint of safety to expose the human body to X-rays of high dose. Therefore, it is desirable that the necessary information in the radiography can be obtained by exposing the human body only once to the X-ray of comparatively low dose. On the other hand, radiographs should preferably have both a wide exposure latitude and high image quality of high contrast, high sharpness, low noise etc. for viewing and diagnosis. Unfortunately, since the conventional radiography is designed to satisfy all the required conditions to some extent, the range of recording density or the ability to record various levels of information and the image quality are both insufficient and neither of these properties are completely satisfied.
In view of the above defects in the conventional radiography, some of the inventors of the present invention have proposed a radiographic image processing method in which the radiographic image is read out by an electronic image read-out device to convert the radiographic image into an electric signal and the electric signal is processed to enhance the diagnostic efficiency and accuracy of the image when the image is reproduced on a recording medium like a photographic film by improving the sharpness and the granularity of the image, as disclosed in Japanese Patent Application No. 53(1978)-28533. This method remarkably improve the diagnostic efficiency and accuracy as compared with the conventional radiography. The details of the method of processing the image, however, were not sufficiently clarified in the above application. On the other hand, with respect to the image quality, it is generally known in the art that the image properties can be changed by processing the image by use of an electronic signal or information processing method. For instance, even in radiography, it is possible to read the image recorded on the X-ray film by an optical scanning means and process the read out signal by a signal processing means to change the various image properties such as contrast and the density level and then record a visible image on a recording film or the like based on the processed signal.
In the radiography, however, the recorded image is used for the purpose of "diagnosis" and the diagnostic efficiency and accuracy (the level of easiness for diagnosis or adaptability to diagnosis) are not simply enhanced by simply making so-called "good" image from the point of the ordinary image quality factors such as sharpness, granularity and contrast. Rather than these factors, the diagnosis efficiency and accuracy are influenced by other complex factors such as reference with the normal pattern, reference with the anatomical structure and utilization of other diagnostic view or records.